This invention relates to electrostatographic reproduction machines, and more particularly to a tandem reproduction machine having a tandem automatic document handler.
Generally, the process of electrostatographic reproduction includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. A charged portion of the photoconductive surface is exposed at an exposure station to a light image of an original document being reproduced. Typically, hard copy jobs, each consisting of a set of sheets of original documents are held and automatically handled by a recirculating document handler to the exposure station. Document handlers used with electrostatographic reproduction machines frequently are provided with a recirculating mode whereby stacked documents are withdrawn individually and sequentially from an input holding tray, passed to the exposure station, and then are outputted back to the holding tray for subsequent recirculation in the previous manner. Some document handlers also invert the documents so that a duplex document may be imaged on both sides.
Exposing a document sheet fed for example by a document handler to the exposure station records an electrostatic latent image onto the photoconductive member. After the electrostatic latent image is recorded as such, the latent image is subsequently developed using a development apparatus by bringing a charged dry or liquid developer material into contact with the latent image. Two component and single component developer materials are commonly used. A typical two-component dry developer material has magnetic carrier granules with fusible toner particles adhering triobelectrically thereto. A single component dry developer material typically comprising toner particles only can also be used. The toner image formed by such development is subsequently transferred to a copy sheet, on which it is then heated and permanently fused in order to form a "hardcopy" of the original image.
Electrostatographic reproduction machines based on this process are now commonly used in business environments, and frequently in a common or central location where a user or users are often required to sequentially reproduce several multiple-sheet hard copy jobs, one after another. Such sequentially produced jobs currently can be pre-programmed or programmed ahead and batched as disclosed, for example, in the following references.
In U.S. Pat. No. 4,834,360 issued May 30, 1989, to Acquaviva, an automatic job batching system is disclosed for a high capacity copier with an RDH (recirculating document handler). The system includes a separate semi-automatic job loading input device for holding and top-down feeding several jobs through a side automatic document handler entrance. It also includes a separate document stacking tray. The jobs are loaded into the input device with slip sheet indicia for controlling the manner in which the jobs are top-down fed and run by the separate single RDH.
In U.S. Pat. No. 4,126,390 issued Nov. 21, 1978, to Connin, a job batching system is disclosed which is a large and complex system including an overhanging rack for automatically sequentially loading separate document jobs and separate programming cover sheets, therefor, into a single RDH tray.
In U.S. Pat. No. 5,081,699 issued Jan. 14, 1992, to Filion et al., a technique for pre-programming a reproduction machine at a console screen is disclosed for a plurality of complex jobs.
Pre-programming of such jobs for reproduction on a reproduction machine at a common or central location is frequently an inconvenient process. This is because users ordinarily have to remove the first hard copy job from a single or sequential job document handler in order to load and run a second such job, pre-programmed or not. It is often the case that a second person (user or operator) wanting to make copies on a conventional machine, upon seeing a first person at the machine, must either wait or go away and return later when they hope the machine would be idle. Even in the case of a single person desiring to reproduce several such jobs, the person ordinarily must wait for the first job to be completed in order to be able to program, load and run a second job.
Some previous attempts to solve this inconvenience problem are disclosed, for example, in the above cited pre-programming and batching references, and in the following additional references.
In U.S. Pat. No. 4,819,023 issued Apr. 4, 1989, to Kitahara, an automatic document feeder (ADF) is disclosed including a reserved feeding station for automatically feeding a plurality of stacks of originals. The ADF includes a reversible first conveyor for conveying documents without inversion to a processing station. The reserved feeding station includes an inverting mechanism for inverting originals being returned to the reserved feeding station.
In U.S. Pat. No. 5,156,386 issued Oct. 20, 1992, to Kitajima et al., an automatic original document feeder (ADF) is disclosed that includes a first sheet path for inverting and guiding an original from a stacker, a second sheet path branching from the first sheet path in a switchback fashion for guiding the sheet to a process position, and a third sheet path branching from the first sheet path in a switch back fashion for discharging the sheet from the process position after inversion.
Additionally, in 1992 , Canon introduced a machine Canon NP-9800 that apparently utilizes the invention disclosed in U.S. Pat. No. 5,156,386 described above. The NP-9800 incorporates an RDF (recirculating document feeder), and a non-RDF second or subfeeder along with a consecutive job programming mode which can be selected only when the machine is operating. The non-RDF subfeeder is used merely for holding the sheets of the second job while a first job is being run from the RDF. Once the first job is completed, the sheets of the second job are moved into the RDF from the subfeeder before they are then run.
There are several disadvantages with this type of system. First, it does not completely solve the problem or the inconvenience of operators waiting. In order to use the subfeeder, all originals or document sheets in the subfeeder and RDF must be the same size, and must be restricted to letter size sheets, fed long edge first. Overall, the design, programming and operation of the limited, non-RDF and RDF feeders of the Canon NP-9800 clearly appear complex and difficult for walk-up, untrained persons.
There is therefore still a need for a reproduction machine that allows a second hard copy job to be programmed at any time, and to be automatically run, even in a recirculatory mode, once a first hard copy job has been run through the exposure station. Importantly, such a machine should offer, in a second RDF, as complete and independent as possible, a set of features that conventionally are only available in the first RDF.